1. Field of the Invention
The present invention relates to a process for preparing an emulsion. More specifically, the present invention relates to a solid particles-containing emulsion which can be suitably used in paints, inks for ink jet printers, fiber-treated agents, coating-materials, adhesives, skin cosmetics, hair cosmetics, and the like.
2. Discussion of the Related Art
As a process for preparing an oil-in-water emulsion in which solid substances useful for liquid droplets are contained, there has been known a process comprising previously adding lipophilic solid particles to be contained to an oil, and thereafter emulsifying and dispersing the resulting mixture (Japanese Patent Laid-Open No. Sho 62-234541). However, in this process, since the viscosity becomes high when the content of the solid substances becomes high, there arise defects that the dispersion of the solid substance is likely to be difficult, and even when the solid substance is emulsified in a solvent incompatible with a solid-liquid mixture, its dispersion is likely to be difficult, so that the ratio of the solid substance cannot be increased.
In addition, when an emulsion prepared by emulsifying and dispersing oil droplets as polymerizable monomers is subjected to suspension polymerization, it is necessary to dissolve a polymerization initiator in a dispersed phase. However, a long period of time is required for dissolving the polymerization initiator in the solid-liquid mixture, and it is difficult to confirm that the polymerization initiator is dissolved. Therefore, there arises a defect that the dispersion of the solid substance is insufficient, because not so much time can be spent for the dispersion of the solid substance in the solution prepared by dissolving the polymerization initiator from the aspect of stability of the polymerization initiator.
An object of the present invention is to provide a process for preparing an emulsion which allows to include solid particles in oil droplets or water droplets (hereinafter simply referred to as xe2x80x9cdispersion dropletsxe2x80x9d); and a process for preparing a solid particles-containing polymer emulsion comprising including a polymerizable monomer in the dispersion droplets of the emulsion, and polymerizing the polymerizable monomer.
Another object of the present invention is to provide a process for preparing an emulsion which allows to include solid particles in the dispersion droplets, wherein the dispersion droplets have a small average particle diameter and are substantially free from agglomerates.
According to the present invention, there are provided:
[1] a process for preparing a solid particles-containing emulsion comprising mixing an oil droplets-in-water emulsion with lipophilic solid particles or a dispersion thereof, thereby allowing to include the lipophilic solid particles in the oil droplets;
[2] a process for preparing a solid particles-containing emulsion comprising mixing a water droplets-in-oil emulsion with hydrophilic solid particles or a dispersion thereof, thereby allowing to include the hydrophilic solid particles in the water droplets; and
[3] a process for preparing a solid particles-containing polymer emulsion comprising including a polymerizable monomer in the water droplets, preparing solid particles-containing emulsion by the process according to item [1] or [2], and polymerizing the polymerizable monomer.
The term xe2x80x9ccontainxe2x80x9d as referred in the present invention encompasses not only the state in which the solid particles are incorporated in the dispersion droplets, but also the state in which a part of the solid particles is contained in the dispersion droplets or the state in which the solid particles are deposited on the surface of the dispersion droplets. In addition, the technical idea of the term xe2x80x9ccontainxe2x80x9d also encompasses the state in which the dispersion droplets are polymer droplets, and the solid particles are deposited to the surface of polymer particles. The solid particles to be contained may be either an inorganic compound or an organic compound.
The term xe2x80x9clipophilic solid particlesxe2x80x9d as referred in the present specification means particles having a surface which forms a contact angle when brought into contact with water. The lipophilic solid particles include those having both lipophilic surface and hydrophilic surface and those in which a hydrophilic surface is surface-treated to give a hydrophilic surface having a lipophilic surface.
The lipophilic solid particles include organic pigments such as monoazo, dis-azo, benzimidazolone, quinacridone, phthalocyanine and other organic pigments; and inorganic pigments such as carbon black. It is desired that the lipophilic solid particles have an average particle diameter of preferably 0.05 to 10 xcexcm, more preferably 0.05 to 5 xcexcm, still more preferably 0.05 to 1 xcexcm, from the viewpoint of the stability of the emulsion.
The term xe2x80x9chydrophilic solid particlesxe2x80x9d as referred in the present specification means particles having a surface which does not form a contact angle when brought into contact with water. The hydrophilic solid particles include those having both hydrophilic surface and lipophilic surface and those in which a lipophilic surface is surface-treated to give a lipophilic surface having a hydrophilic surface.
The hydrophilic solid particles include titanium oxide, silica, zeolite, barium sulfate, calcium carbonate, kaolin, iron oxides, and the like. It is desired that the hydrophilic solid particles have an average particle diameter of preferably 0.05 to 10 xcexcm, more preferably 0.05 to 5 xcexcm, still more preferably 0.05 to 1 xcexcm, from the viewpoint of the stability of the emulsion.
When the solid particles are used in a form of dispersion, a dispersing agent for dispersing the solid particles is used as occasion demands.
The dispersing agent includes anionic surfactants such as dodecylsulfates, dodecylbenzenesulfonates, and sulfates of polyoxyethylene nonyl phenyl ethers; nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, polyoxyethylene-polyoxypropylene block copolymers, and sucrose ester of fatty acids; cationic surfactants such as octadecyltrimethylammonium chloride; amphoteric surfactants such as alkyl dimethylaminoacetate betaines and 2-alkyl-N-carboxy-N-hydroxyimidazolium betaines; natural or synthetic high-molecular compounds such as polyvinyl alcohols, gelatin, polyvinyl pyrrolidones, polymethyl vinyl ethers, polybutadienes, proteins, hydroxyalkyl celluloses, polyurethane resins, and acrylic resins, and the like.
The component in the oil phase and the component in the water phase used during the preparation of an O/W or W/O emulsion are selected so that these components are incompatible with each other.
The component in the oil phase incompatible with water is preferably an organic compound having a solubility to water of not more than 1 g per 100 g of water at 20xc2x0 C. The organic compound includes cyclohexane, n-hexane, benzene, cottonseed oil, rapeseed oil, squalane, squalene, waxes, styrene, divinylbenzene, butyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, decyl acrylate, lauryl acrylate, dodecenyl acrylate, myristyl acrylate, palmityl acrylate, hexadecenyl acrylate, stearyl acrylate, octadecenyl acrylate, behenyl acrylate, butyl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate, decyl methacrylate, lauryl methacrylate, dodecenyl methacrylate, myristyl methacrylate, palmityl methacrylate, hexadecenyl methacrylate, stearyl methacrylate, octadecenyl methacrylate, behenyl methacrylate, silicone macromonomers, and the like.
The component in the water phase incompatible with the component in the oil phase includes water alone, and water solutions prepared by dissolving optional necessary ingredients in water.
When an emulsion is prepared, there can be used a dispersing agent such as the surfactants and the natural and/or synthetic high-molecular compounds listed above as occasion demands.
When allowing to include solid particles in oil droplets of an O/W emulsion, lipophilic solid particles are used. Alternatively, there can be used lipophilic solid particles prepared by treating the surface of hydrophilic solid particles with a surface modifier to impart lipophilicity to the surface.
On the other hand, when allowing to include the solid particles in the water droplets of a W/O emulsion, hydrophilic solid particles are used. Alternatively, there can be used hydrophilic solid particles prepared by treating the surface of lipophilic solid particles with a surface modifier to impart hydrophilicity to the surface.
It is preferable that the lipophilic solid particles have substantially non-polar surfaces, and show little interactions with water molecules (easily to be wetted with water).
In addition, it is preferable that the hydrophilic solid particles have a largely polar surface, and show large interactions with water molecules (easily wetted with water).
The surface modifier includes anionic surfactants such as dodecylsulfates, dodecylbenzenesulfonates, and sulfates of polyoxyethylene nonyl phenyl ethers; nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, and polyglycerol fatty acid esters; cationic surfactants such as octadecyltrimethylammonium chloride; amphoteric surfactants such as alkyl dimethylaminoacetate betaines, 2-alkyl-N-carboxy-N-hydroxyimidazolium betaines and lecithin; coupling agents such as phosphate coupling agents, silane coupling agents, and titanate coupling agents; high molecular-coating surface modifiers such as polydimethyl siloxanes, and the like. These surface modifiers can be used for either of a case where the surface of the lipophilic solid particles is modified to have hydrophobicity or a case where the surface of the hydrophilic solid particles is modified to have lipophilicity.
First, a process for preparing a solid particles-containing emulsion comprising preparing an O/W emulsion, and mixing the resulting emulsion with lipophilic solid particles or a dispersion thereof, thereby allowing to include the lipophilic solid particles in the oil droplet will be explained.
An O/W emulsion is prepared by mixing a component in the water phase prepared by dissolving a dispersing agent in water with a hardly water-soluble component in the oil phase, and emulsifying the mixture. As the means for emulsification, there can be preferably employed shearing machines, including high-speed shearing emulsifiers such as homomixers, ultratalacs and milders, and high-pressure homogenizers; ultrasonic wave emulsifiers, and the like. The ratio of the component in the oil phase to the component in the water phase may be a given value, and it is preferable that the ratio of the oil phase is 0.5 to 50% by weight, from the viewpoint of operability. It is preferable that the dispersion droplets of the emulsion have an average particle diameter of 0.1 to 30 xcexcm. The average particle diameter is more preferably 0.1 to 10 xcexcm, from the viewpoint of narrowing the particle diameter distribution of the dispersion droplets of the solid particles-containing emulsion after allowing to include the lipophilic solid particles in the component in the oil phase. The average particle diameter of the dispersion droplets of the emulsion can be determined by using a laser scattering particle diameter analyzer xe2x80x9cLA-910xe2x80x9d commercially available from Horiba, LTD.
The O/W emulsion obtained in the manner described above is mixed with lipophilic solid particles or a dispersion thereof. The lipophilic solid particles may be either organic particles or inorganic particles. An embodiment of addition of the particles is not limited to specified ones. When the diameter of the particles is small, it is desired to use the lipophilic solid particles in the form of a water dispersion prepared by dispersing the lipophilic solid particles in a component in the water phase, because it would be difficult to homogeneously disperse the lipophilic solid particles when added in the form of powder. A process for dispersing the lipophilic solid particles in the component in the water phase may be a known process, and a dispersing agent can be used during dispersion as occasion demands.
The solid particles-containing emulsion can be obtained by mixing an O/W emulsion with the lipophilic solid particles or a dispersion thereof to migrate the lipophilic solid particles existing in the component in the water phase to the component in the oil phase, thereby allowing to include the lipophilic solid particles in the oil droplets.
The amount of the lipophilic solid particles contained in the oil phase is preferably 0.5 to 80 parts by weight, and more preferably 1 to 50 parts by weight, based on 100 parts by weight of the component in the oil phase, from the viewpoint of the stability of the emulsion.
The means for allowing to include the lipophilic solid particles in the component in the oil phase may be simply bombardment of the solid particles with the oil droplets by means of agitation, or the like. From the viewpoint of more rapidly and securely allowing to include the lipophilic solid particles in the component in the oil phase, it is preferable to apply a shear to the oil droplets to finely divide the oil droplets, thereby making it possible to increase a contact frequency of the oil droplets and the solid particles. In addition, when the oil droplets are finely divided, their surface areas are increased, so that the amount of the dispersing agent relative to the finely divided particles is deficient, thereby having an unstable state. However, since the finely divided liquid droplets are unified into one body, the unified droplet becomes a stable state, and the solid particles are incorporated into the oil droplets during the unification.
The means for applying a shear include high-speed shearing emulsifiers such as homomixers, milders and colloidal mills, and high-pressure homogenizers; and the means for applying ultrasonic waves include ultrasonic wave emulsifiers, without being limited thereto as long as a shearing force or ultrasonic waves are applied to the mixture. Among them, it is preferable to use high-speed shearing emulsifiers such as homomixers, milders, colloidal mills, and ultratalacs, filmics, or high-pressure homogenizers, from the viewpoint of productivity. It is preferable that the shearing force is not less than 50 Pa in order to adjust the content of the solid particles to a practically desirable level of not less than 40% by weight. It is desired that the shearing force is not less than 100 Pa, from the viewpoint of more rapidly including the solid particles.
In the present invention, the shearing force is expressed by the equation (I):
xcfx84=xcexcxc2x7Sxe2x80x83xe2x80x83(I)
wherein xcexc is viscosity (Paxc2x7s) of a fluid; and S is a shear rate expressed by the equation (II):
S=du/dyxe2x80x83xe2x80x83(II)
wherein u is a linear velocity (m/s) [when a high-speed shearing emulsifier is used, the linear velocity corresponds to a tip speed of a rotatable part; and when a high-pressure homogenizer is used, the linear velocity corresponds to a velocity of the fluid flowing through the homogenizing valve; and when a mixing vessel is used, the linear velocity corresponds to a peripheral speed of a tip end of agitation impellers]; and y is a distance (m) in a direction perpendicular to a migrating surface [when a high-speed shearing emulsifier is used, the distance corresponds to a distance from a tip end of a rotor to a stator; when a high-pressure homogenizer is used, the distance corresponds to a gap between the homovalves through which the fluid passes; and when a mixing vessel is used, the distance corresponds to a distance from a tip end of agitation impellers to a vessel wall].
It is preferable that the shearing rate is not less than 50xc3x97103 sxe2x88x921, in order to more efficiently adjust the content of the solid particles to not less than 40% by weight, and it is more preferable that the shearing rate is not less than 100xc3x97103 sxe2x88x921, from the viewpoint of rapidly allowing to include the solid particles in the droplets. In addition, it is preferable that the shearing rate is not more than 150xc3x97103 sxe2x88x921, from the viewpoint of adjusting the content of the solid particles to not less than 50% by weight, and it is preferable that the shearing rate is not more than 100xc3x97109 sxe2x88x921, from the viewpoint of avoiding the destruction of the solid particles or agglomeration of the solid particles. Incidentally, when the ultrasonic waves are utilized, it is desired that shearing is carried out at an output of not less than 3 kW/m2.
Next, a process for preparing a solid particles-containing emulsion comprising mixing the W/O emulsion with hydrophilic solid particles or a dispersion thereof, thereby including the hydrophilic solid particles in the water droplets will be explained.
A W/O emulsion is prepared by mixing a hardly water-soluble component in the oil phase in which the dispersing agent is dissolved with water or a component in the water phase prepared by dissolving a water-soluble component in water, and emulsifying the mixture. The emulsification process may be the same as the process when the O/W emulsion is prepared. The ratio of the component in the water phase to the component in the oil phase may be optionally selected, and it is preferable that the ratio of the water phase is 0.5 to 50% by weight, from the viewpoint of operability. The dispersion droplets of the emulsion have an average particle diameter of preferably 0.1 to 30 xcexcm, and more preferably 0.1 to 10 xcexcm from the viewpoint of narrowing the particle diameter distribution of the dispersion droplets of the solid particles-containing emulsion after allowing to include the hydrophilic solid particles in the component in the water phase. The average particle diameter of the dispersion droplets can be determined in accordance with the same method as above.
The W/O emulsion obtained in the manner described above is mixed with hydrophilic solid particles or a dispersion thereof. The hydrophilic solid particles may be either organic particles or inorganic particles. An embodiment of addition of the particles is not limited to specified ones. When the diameter of the particles is small, it is desired to use the hydrophilic solid particles in the form of an oil dispersion prepared by dispersing the hydrophilic solid particles in a component in the water phase, because it would be difficult to homogeneously disperse the hydrophilic solid particles when added in the form of powder. A process for dispersing the hydrophilic solid particles in the component in the oil phase may be a known process, and a dispersing agent can be used during dispersion as occasion demands.
The solid particles-containing emulsion can be obtained by mixing a W/O emulsion with the hydrophilic solid particles or a dispersion thereof to migrate the hydrophilic solid particles existing in the component in the oil phase to the component ir the water phase, thereby allowing to include the hydrophilic solid particles in the water droplets.
The amount of the hydrophilic solid particles contained in the component in the water phase and the means for applying a shearing force or ultrasonic waves when the average particle diameter of the dispersion droplets is not less than 1 xcexcm may be the same as those of the preparation of the solid particles-containing emulsion using the W/O emulsion.
In addition, when an O/W emulsion is used, the solid particles-containing polymer emulsion can be obtained by including the lipophilic solid particles in oil droplets comprising lipophilic polymerizable monomers and an oil-soluble polymerization initiator, and polymerizing the polymerizable monomers. On the other hand, when a W/O emulsion is used, the solid particles-containing polymer emulsion can be obtained by including the hydrophilic solid particles in water droplets comprising hydrophilic polymerizable monomers or a mixture comprising water and hydrophilic polymerizable monomers, and a water-soluble polymerization initiator, and polymerizing the polymerizable monomers.
When either an O/W emulsion or a W/O emulsion is used, the core-shell type solid particles-containing polymer emulsion can be obtained by including the polymerizable monomers in the continuous phase, and polymerizing the polymerizable monomers in the dispersed phase and concurrently polymerizing the polymerizable monomers in the continuous phase.
The lipophilic polymerizable monomers are preferably those having a solubility to water of not more than 1 g per 100 g of water at 20xc2x0 C. The lipophilic polymerizable monomers includes, for instance, styrene, divinylbenzene, butyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, decyl acrylate, lauryl acrylate, dodecenyl acrylate, myristyl acrylate, palmityl acrylate, hexadecenyl acrylate, stearyl acrylate, octadecenyl acrylate, behenyl acrylate, butyl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate, decyl methacrylate, lauryl methacrylate, dodecenyl methacrylate, myristyl methacrylate, palmityl methacrylate, hexadecenyl methacrylate, stearyl methacrylate, octadecenyl methacrylate, behenyl methacrylate, silicone macromonomers, and the like. These lipophilic polymerizable monomers may be used alone or in admixture of two or more kinds.
The hydrophilic polymerizable monomers include unsaturated carboxylic acid monomers such as acrylic acid, methacrylic acid, itaconic acid and maleic acid; unsaturated sulfonic acid monomers such as styrenesulfonic acid, 2-acrylamide-2-methylpropane sulfonic acid, 3-sulfopropylacrylate, 3-sulfopropylmethacrylate, and vinylsulfonic acid; unsaturated phosphate monomers, such as vinyl phosphate, diphenyl-2-acryloyloxyethyl phosphate and diphenyl-2-methacryloyloxyethyl phosphate; N,N-dimethylacrylamide, and the like. These hydrophilic polymerizable monomers can be used alone or in admixture of two or more kinds.
As the oil-soluble polymerization initiator, there can be generally used those which initiate addition polymerization of the monomers by radical decomposition with heating or in the presence of a reducible substance. The oil-soluble polymerization initiator includes, for instance, organic peroxides such as lauroyl peroxide and benzoyl peroxide; and azo compounds such as 2,2xe2x80x2-azobisisobutyronitrile, 2,2xe2x80x2-azobis(2,4-dimethylvaleronitrile) and 2,2xe2x80x2-azobis(2-methylbutyronitrile). These polymerization initiators may be used alone or in admixture of two or more kinds.
The water-soluble polymerization initiators are those which initiate addition polymerization of the monomers by radical decomposition with heating or in the presence of a reducible substance. There can be generally used water-soluble peroxodisulfates, peroxides, azobis compounds, and the like. The water-soluble polymerization initiator includes, for instance, peroxodisulfates such as potassium persulfate and ammonium persulfate; peroxides such as hydrogen peroxide and t-butyl hydroperoxide; and azo compounds such as 2,2xe2x80x2-azobis-2-amidinopropane salt and 4,4xe2x80x2-azobis-4-cyanopentanoic acid. The water-soluble polymerization initiator can also be used as a redox initiator by using together with a reducing agent.
The solid particles-containing polymer emulsion obtained by the present invention can be suitably used for, for instance, paints, inks for ink jet printers, fiber-treated agents, coating materials, adhesives, skin cosmetics, hair cosmetics, and the like. Specifically, the solid particles-containing polymer emulsion is suitable for skin cosmetics, hair cosmetics, and the like.